How to use Portland cement

HOW TO USE

Portland Cement

From the German of L. GOLINKLLI.

Published under the name of ^^ Das Kleine Cement- Buck ^'^
by the Association of German Portland
• Cement Manufacturers.

Translated by

SPENCER B. NEWBERRY, E. M. Ph. D.,

Acting Professor of Chemistry, Cornell University, 1887-1S92.

U. S. Commissioner to Paris Exposition, 1889

Judge, Chicago Exposition, 1893.

Copyrighted by W1LI.IAM SeaFERT,
1899

THIRD EDITION 1904

Price^ Fifty Cents*

LA '4

Cement and Engineering News
CHICAGO,

IN PREPARATION

TREATISE ON

Armored Concrete Constructions

With General Applications under the Various Systems in use in the United States and
Europe, with numerous illustrations and calculations.

BY E. I_EE HEIDENFIEIC^H

Member American Institute Mining Engineers aud Western Society of Engineers.

[Copyright 1903]

SYNOPSIS OF

Chapter I. Abbreviated history.

Chap. II. Cause of the extraordinary de-
velopment of Armored Concrete.

Chap. III. Illustrated applications of the
principal systems of Floor Constructions,
Beams, Girders and Foundations.

Chap. IV. Illustrated application of the
principal systems of Culverts, Pipes and Tun-
nel Construction,

Chap. V. Tanks and Reservoirs.

Chap. VI. Cluster Construction, G''ain
Elevators, Cement and other storage.

Chap. VII. Retaining Walls, Docks and Chap. XIX

Wharves. Chap. XX.

Chap. VIII. Arches and Domes. Appliances

Chap. IX. Bridges. Chap. XXI.

Chap, X. Stairs, Grand Stands, Etc. Construction

Chap. XI. Manufactured Articles, Fence Chap. XXII

Posts, Smoke Jacks, Coffins, Tubs, Small Cul tails
vert and Sewer Pipe, etc. Chap. XXIII

Chap. XII. Application of Moulds and Chap. XXIV

CONTENTS.

Chap. XIII. General notes on the Relative
and Combined Strength of Steel and Concrete.

Chap. XIV. Calculation of Floor Beams
and Girders.

Chap. XV. Calculation of Columns and
Piers.

Chap. XVI. Calculation of Pipes, Culverts,
Arches and Domes.

Chap. XVII. Calculation of Tanks, Re-
servoirs and Clusters.

Chap. XVIII, Calculation of Retaining
Walls.

Calculation of Bridges.
Practical Details, Tools and

Cost of Armored Concrete

Miscellaneous Practical De-

General Conclusion.
Index.

Centers.

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\ Treatise on the use of Concrete and Steel

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HOW TO USE

Portland Cement.

From the German of L. Golinelli.

Published under the name Das kleine Cement-buch by the Association of
German Portland Cement Manufacturers.

Translated by Spencer B. Newberry. ",€, Ilewbvvrv)

[Copyrighted by William Seafert.]
1899.

CHICAGO:

CEMENT AND ENGINEERING NEWS,

190S.

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.Gr6z

6

PREFACE.

A few years ago a very important and useful book,
"Der Portland-cement und seine Anwendungen im
Bauwesen," (Berlin, 1892), was published by the Asso-
ciation of German Portland Cement Manufacturers.
This work includes the best information obtainable in
reference to the testing and uses of Portland cement,
and contains numerous illustrations showing the details
of important examples of engineering work in which
cement was employed. The cordial reception given
this book by educated engineers led the association
to undertake the preparation of a small pamphlet on
the same subject, intended chiefly for the use of con-
tractors and masons, which should give in simple and
practical form the results of the best experience in the
use of Portland cement. This pamphlet has lately been
issued under the title of " Das Kleine Cement-buch,''
by the publishers of the Thonindusii'ie Zeitung. Over
22,000 copies were sold in Germany during the past
few months, and a new edition has already been ordered.

Germany has long led the world in knowledge of
the applications of cement, and most of our best
information in regard to methods of manufacture,
testing and uses of cement has come from that coun-
try. A full translation of this little pamphlet, repre-
senting, as it does, the latest German thought on the
subject, will therefore doubtless be of interest to Amer-
ican cement consumers.

S. B. N.
Sandusky, O., March, 1899

HOW TO USE PORTLAND CEMENT.

From the German of L. Golinelli.

(Published under the name Daskleine Cement-buchhj the Asso-
ciation of German Portland Cement Manufacturers.)

Translated by S. B. Newbbbby.

It is an established fact that Portland cement is
superior to all other hydraulic materials, natural or
artificial, and for this reason it is widely distributed
throughout the world. Its use would, however, be far
greater if the knowledge of the applications and meth-
ods of testing of cement had kept pace, during the past
ten years, with the improvements which have been
made in quality and methods of manufacture. Even
in sections where the manufacture of Portland cement
has been extensively and successfully developed, and
where one would consequently expect to find a certain
amount of knowledge of the subject, a correct under-
standing of methods of testing and intelligent use of
cement is often painfully lacking. The preparation and
use of cement mortar, as practiced in many cases by
masons or their helpers, is not only imperfect but
wasteful. Better work could often be done with less
material if careful methods were used. In the case of
Portland cement such careful methods are especially
necessary and profitable, and if thej^ were followed the
common complaint that Portland cement is too expens-
ive would soon be no longer heard. Those who do
intelligent and careful work have for a long time recog-
nized the injustice of this charge. On the other hand,
it is undoubtedly true that a high-grade material like

6 PBOPEBTIES OF PORTLAND CEMENT.

Portland cement, which in skillful hands may be use-
fully and economically employed for an immense vari-
ety of purposes, is especially liable to suffer from ignor-
ance and misuse.

I. PROPERTIES OF PORTLAND CEMENT.
DEFINITION AND MANUFACTURE.

Portland cement is a material which hardens in the
presence of water, prepared by burning at a sintering
temperature an intimate mixture consisting essentially
of lime (or carbonate of lime) and clay in certain defin-
ite proportions.

The raw materials, clay and carbonate of lime, are
ground and mixed according to their character in either
the wet or dry way. If the dry process is used, the
mixed materials are moistened with water and molded
into blocks. In the wet process the bricks are made
from the wet material after it has been reduced to the
proper consistency. After drying, the bricks of cement
material are burned in suitable kilns to the point of
sintering. The resulting "clinker" is ground to a fine
powder; this is the finished cement.

CHEMICAL COMPOSITION.

The raw materials indicate the nature of the constit-
uents of Portland cement. These are silica, alumina,
iron oxide, lime and a small amount of magnesia.
Alkalies and sulphates are are also always present, and
are derived from the raw materials, which are never
found pure in nature.

The presence of sulphuric acid (sulphate of lime) is
also due to the sulphur in the fuel employed, and to
the addition of a small amount of gypsum (sulphate of
lime) for the purpose of making the cement slow-setting.

CHEMICAL COMPOSITION. 7

The composition of good Portland cement usually

Taries between the following limits:

Lime 58 to 65 per cent

Silica 20 to 26

Alumina 7 to 14

Magnesia 1 to 3

Alkalies traces to 3

Sulphuric Acid traces to 2

According to the character of the raw material used,
each manufacturer determines the correct composition
of his product within the above limits, and this com-
position must be kept uniform by constant chemical
analysis. The widespread belief that defective quality
of cement is due to bad raw materials is seldom well
founded; the fault is generally due to incorrect propor-
tions and careless manufacture.

In studying the qualities of Portland cement, the
following points are to be especially noted :

1. Form and fineness of grain.

2. Color and specific gravity.

3. Time of setting.

4. Hardening.

5. Strength.

6. Constancy of volume.

7. Hair cracks and shrinkage cracks.

8. Behavior under under extreme heat and cold.

9. Additions and adulterations.

FORM AND FINENESS OF GRAIN.

When examined under the microscope, particles of
hydraulic lime have a more or less rounded form.
Portland cement, on the other hand, shows thin leaf-
lets of shale-like structure, like pounded glass. The
high quality of Portland cement is in part due to this
shale-like character, since greater density of mortar

8 COLOR AND SPECIFIC GRAVITY.

results from the greater surface of contact and smaller
proportion of voids between the particles.

As to fineness of grinding, it may be mentioned that
the coarser particles of cement act practically like sand.
It is therefore important that the grinding be not too
coarse. A residue of not more than 5 per cent on a
sieve of 75 meshes to the linear inch may fairly be
demanded. The finer the grinding, the more sand can
be used with the cement. It should be remembered,
however, that poor cements, especially those too high
in clay or imperfectly burned, are especially easy to
grind to great fineness. Such cements may be gener-
ally recognized by their yellowish color and the spotty
appearance of the work.

COLOR AND SPECIFIC GRAVITY.

The color of Portland cement should be a greenish
gray; a yellowish or reddish gray tint indicates gener-
ally an inferior, light-burned product, or one to which
under-burned or " dusted " material has been added.

Portland cement has a high specific gravity, a quality
which contributes to its high value. No other hydraulic
material has so high a specific gravity, or yields so
dense and resistant a mortar. The specific gravity of
Portland cement is from 3.12 to 3.25.

TIME OF SETTING.

When Portland cement is mixed with a suitable qual-
ity of water, a plastic paste is produced, which after a
time becomes hard. The change from a semi-liquid to
a solid mass is called setting, and the time required for
%is change, the time of setting. Cement is said to be
set when it resists a light pressure of the finger nail on
the surface.

TIME OF SETTING. 9

It is of the greatest importance to know the time
of setting of a cement which it is proposed to use, since
a cement which has become set and has been again
mixed up with water possesses little or no hydraulic
energy. The mistake of mixing "set*' mortar anew
with water occurs only too often, and gives rise to the
unjust complaint that the cement does not harden or
possesses no strength. Great care should therefore be
taken to mix up only such a quantity of mortar as can
be conveniently used up in the time available; this can
be easily managed when the time of setting is known.

Remnants of mortar which have become set should he
discarded and must under no circumstances he again
worked up with water.

The determination of the time of setting is extremely
simple, and may be made by any mason at the place
where the cement is used. The best method is as fol-
lows:

The cement is mixed with water to a thick paste,
worked one to two minutes with a spoon or trowel and
spread out in the form of a pat on a glass plate. This
pat should be about one-half inch thick in the middle
and thin at the edges. As soon as the surface resists a
light pressure of the finger-nail the cement is set.
Since the temperature and the proportion of water
used are of great influence on the result, it is best to
have the cement and water at the ordinary temperature
of 60 to 70 degrees, and to use not more than 30 to 32
per cent of water. The water must be clean. The pat
should be protected from sunshine and drafts of air.

It is in the power of the manufacturer to produce
either quick-setting or slow-setting cement, as may be
required. A cement which requires two hours or longer
to set is called slow-setting. Such cement is preferable

10 HARDENING.

to that which sets quickly, on account of its greater
strength. Quick-setting cement is used only for cer-
tain special purposes. Slow-setting cement can be
made to set more quickly by using warm water, and
also by limiting the water used to the smallest possible
quantity. Among the substances which modify the
time of setting may be mentioned:

Potash and soda, which hasten the setting. Sulphates
and calcium chloride, which retard the setting.

In all cases the consumer will do well to notify the
manufacturer what time of setting is desired, also for
what purpose the cement is to be used. In this way
many unjust complaints in regard to quality and many
unnecessary expenses may be avoided.

HARDENING.

The set cement is capable of hardening^ either in
water or in air, and in a short time will acquire a high
degree of strength. The processes of setting and hard-
ening should not be confused. The latter begins at the
point where the former ceases, and continues up to the
highest strength which the cement attains after the
lapse of many years.

As to the nature of the hardening process, to account
for which various theories have been advanced, it need
only be here stated that the hardening consists in chem-
ical combination with water taking place under certain
physical conditions. Among the most important of
these conditions are rest during the setting and protec-
tion from too rapid drying out. The latter point can
not be too strongly insisted upon. If the cement is
deprived of the necessary water it can never reach its
full hardness.

STRENGTH. 11

Portland cement attains within a few days a high
degree of strength.

In the use of cement for building purposes, compres-
sion strength is the quality generally required. Cement
is, however, generally tested only for tensile strength,
owing to the fact that the tests of tensile strength can
be made much more quickly, simply and cheaply than
those of compression. There is also a definite, (though
by no means exact) relation between the two tests, the
compression strength being generally from 8 to 12
times the tensile strength.

The German official standards for Portland cement
require that a mixture of one part cement with three
parts normal sand shall show a tensile strength at 28
days of at least 227 lbs. per sq. in.

It is by no means simple, however, to make tensile
strength tests in such a manner as to give reliable
results. Complaints in regard to the quality of cement
are often due entirely to faulty testing. In the prepar-
ation of briquettes, the temperature and quantity of the
water used, the character of the sand employed, and
the thoroughness with which the mortar is worked, are
of immense influence on the results. The strength will
generally be greater the less water is used; nevertheless
it is always necessary to use such a quantity of water
that it shall show itself on the surface of the briquette
on tamping it into the mold. Long and vigorous work-
ing of the mortar increases its strength. In extensive
building operations the use of mixing machines, especi-
ally pans with edge runners, is therefore highly advan-
tageous.

CONSTANCY OF VOLUME AND CRACKING.

Strictly speaking, there is no such thing as constancy
of volume, either in the case of mortar or stone, since

12 CONSTANCY OF VOLUME AND CRACKING.

heat and cold, wetting or drying, modify the volume
more or less. Portland cement also suffers changes of
volume on hardening in water or in air. In the case of
good Portland cement, however, these changes are
extremely small and much less than those which occur
in different kinds of stone. Bad cements, on the other
hand, may show the dangerous quality of cracking or
swelling. This shows itself in a strong expansion,
which destroys the cohesion of the mortar and may
cause its total destruction. Cement which swells badly,
if laid between retaining walls, shows an immense
power of expansion, even to the extent of forcing out
the stones of the masonry.

The swelling does not show itself until after the set-
ting. The worse the fault is the sooner it will appear.
It shows itself, also, sooner in water than in air. In
pats of cement kept under water this defect is to be
noticed in the appearance of fine net-like cracks, or in
worse cases in curving of the pats and the appearance
of cracks around the edges. It is characteristic of
expansion cracks that they run from the edges toward
the center of the pat and are widest at the edges and
narrower toward the center. These expansion cracks
should not be confused with shrinkage cracks, mention
of which will be made later.

The swelling of cement is always due to defects in
manufacture. These are:

1. Faulty composition of the raw material, especi-
ally too high a proportion of lime.

2. Imperfect preparation of the raw material.

3. Imperfect burning of the clinker.

4. Too high proportion of sulphate or magnesia.
According to the German oflScial requirements, a

cement is considered to be constant in volume if a pat.

SHRINKAGE-CRACKS AND HAIR-CRACKS. 13

kept 28 days under water, remains perfectly flat and
free from cracks. Swelling, due to too much lime,
shows itself in this test with certainty within a few
days or weeks. Cement containing too much magnesia,
however, and burned to the point of sintering, shows
noticeable expansion only after the lapse of long peri-
ods, extending even to several years. Only chemical
analysis, or the guarantee of the manufacturer, can
afford protection against the danger of expansion from
excess of magnesia. Experience has shown that the
presence of magnesia up to 3 per cent is entirely harm-
less.

In conclusion, two other peculiar appearances may
be mentioned which are often erroneously considered
to indicate swelling of the cement.

It is sometimes noticed that pats of neat cement,
left in air, lose considerably in strength, and after a
certain time become soft or friable, while similar pats
kept in water are faultless in all respects. This is espe-
cially liable to occur in the case of pats made very wet
and allowed to dry out immediately after setting. If,
on the other hand, the pats are kept moist during th»
first stages of hardening, this defect is not developed.

Cracks, similar to those produced by swelling, are
also produced when pats or briquettes are placed in
water too soon^ or before the setting is complete. To
prevent this the official requirements specify that test-
pieces shall be kept 24 hours in moist air before placing
in water.

SHRINKAGE-CRACKS AKD HAIR-CRACKS.

Portland cement mortar without sand, exposed to the
air, diminishes in volume. If the drying takes place
gradually and uniformly, as in a closed room, the
cement shows no defects. Too rapid drying, in draughts

14 RESISTANCE TO WEATHER.

of air or in sunshine, without the precaution of keeping
the cement moist, causes so-called shrinkage-cracks.
These may be distinguished, in pats of cement, from
expansion-cracks by the fact that they appear during
the setting and show themselves as irregular curved
lines extending over the middle of the pat. As already
stated, the formation of shrinkage cracks is due to
faulty use of the cement, and has practically nothing to
do with its quality. Very finely ground cements are,
moreover, more likely to show hair-cracks than those
which are more coarsely ground.

Hair-cracks appear as fine lines on cement work
which has stood some time. They are especially to be
noticed on cement which has lain in the open air, and
are due to frequent changes between wet and dry con-
ditions. Hair-cracks and shrinkage-cracks occur chiefly
when pure cement or mortar too rich in cement is used.
They may be certainly avoided by the addition of suflS-
cientsand and suitable treatment of the work.

RESISTANCE TO WEATHER AND REHAVIOR UNDER EXTREME
HEAT AND COLD.

Mortar made from pure cement is, strictly speaking,
not weatherproof, owing to its tendency to form shrink-
age-cracks and hair-cracks. Repeated expansion and
shrinkage increases the number and size of these cracks,
until finally under the action of water and frost the
cement breaks to pieces. Complete weather-resisting
qualities can be given to cement mortar only by the
the addition of sand. One part sand to one part cement
will be found sufficient.

The temperatures which are reached in warm, or
even hot, climates have no bad influence on the harden-
ing of Portland cement. The only precaution necessary

BEHAVIOB UNDER EXTREME HEAT AND COLD. 15

is to see that the water necessary for hardening is not
removed too soon; or, in other words, that the work is
kept sufficiently moist during the earlier stages of hard-
ening. Even the temperature of boiling water is harm-
less to the strength of Portland cement, and a heat of
400 degrees to 500 degrees F. may be borne without in-
jury. At a red heat it becomes soft and friable. Never-
theless it has been proved by long experience with
Portland cement concrete that this material shows a
high degree of strength and safety when exposed to fire.
Portland cement is less affected by frost than any
other hydraulic material; If the cement is once fully
set it may be exposed to strong freezing without any
ill effect. It is only during the setting that injury can
take place, and this is chiefly to be feared in case the
mortar was made too wet, so that the freezing of the
water forces the mass asunder. If water is sparingly
used, masonry and concrete work may be done in
extremely cold weather with good results. It must be
remembered, however, that the setting and hardening
of cement are much delayed by cold. Cement work
done in freezing weather shows, therefore, but little
strength at first, but finally reaches its normal hardness.
Addition of salt to mortar in cold weather is generally
to be avoided on account of the unsightly efflorescences
which often result. It is better, when work in extreme
heat or cold cannot be avoided, to warm the water
and sand used and to reduce the water to the small-
est possible quantity in order to hasten the setting of
the mortar. If care is taken to allow no free water to
separate, or that any excess of water is absorbed by dry
stone, there is nothing to be feared even from extreme
eold. Surface plastering with cement should, how-
ever, not be attempted in freezing weather.

16 ACTION OF SEA WATEB.

On mixing cement with sea water the setting is
delayed and decreased strength results. This is chiefly
due to the action of the magnesium sulphate and chlor-
ide of the sea water on a portion of the cement; the
hardening value of this part is therefore lost and the
strength !:ttained is less than with the use of fresh
water. One might suppose that this action of the sea
water salts would cause the strength of the cement to
continue to fall off and that the work would finally
fall to pieces. This is, however, not the case, owing to
the fact that the penetration of the sea water into the
mass is prevented by the great and constantly increasing
density of the Portland cement mortar. A deposit of
magnesia is also formed in the pores of the mass, and
gives further protection against the entrance of the
sea water. Portland cement is therefore unequalled
for marine constructions. In all cases in which this
work has been intelligently done Portland cement con-
crete has fulfilled all requirements most satisfactorily.
In work exposed to sea water it is of the highest
importance to give the concrete as dense and close-
grained a surface as possible, since only such a surface
is capable of permanently resisting the chemical action
of the salt water and the mechanical force of the waves.

Portland cement is especially suitable for work of
this kind, since uniform tests of tensile and compres-
sion strength are a guarantee of a uniform material
which can safely be relied upon. This is by no means
true in the case of puzzuolana cements, so-called slag
cements and hydraulic limes, which are often of very
variable quality.

ADDITIONS AND ADULTEBATIONS.

Substances added to Portland cement may be divided
into those which are intended to give it certain valuable

ADDITIONS AND ADULTERATIONS. 17

qualities, and others which are added for the purpose
of fraud. In the first group are found gypsum and
coloring matters.

The addition of gypsum (sulphate of lime) which
should not exceed 2 per cent, is made for the purpose
I of causing naturally quick-setting cements to set more

slowly. In this way the quality of the cement is
improved and its strength increased. Additions of a
higher proportion of gypsum are not admissable, as it
tends to cause swelling.

Coloring matters are sometimes added to cement in
order to make it suitable for decorative purposes.
Mineral colors are practically always used. To give the
cement a somewhat darker tint, especially for use in
making cement wares, a few per cent of lamp-black
is added. Nearly all coloring matters reduce the
strength of the cement; ultra-marine, however, in small
quantities, increases it. The red iron oxide of com-
merce, often used to produce a red color, frequently
contains a considerable amount of sulphuric acid, and
may cause swelling. Care should be taken in the
choice of the coloring matters employed.

In regard to the production of white Portland cement
it may be said that this has not hitherto proved success-
ful, on account of impurities contained in the raw
materials or derived from the fuel. The so-called
white cements of commerce are for the most part
inferior products which do not deserve the name of
Portland cement. In consequence of its gray color,
Portland cement cannot be made white by the addition
of pigments.

From fraudulent and avaricious motives, blast furn-
ace slag, limestone, shale, basalt, ashes, sand, etc, aro
added to cement. These are simply adulterations,

18 PACKING AND WEIGHT. — SEASONING.

which always injure the quality of the product. These
substances may be more or less easily detected, and
their use, in consequence of the close watch kept by
the association upon the product of its members, has of
late practically ceased.

II. USE OF PORTLAND CEMENT.
PACKING AND WEIGHT.

(American weights are here substituted for the German weights
given in the original pamphlet. — Tbanslator.)

Portland cement is packed in barrels and sacks. The
barrel is of 400 lbs. weight and contains 380 lbs. (about
3 J cubic ft.) of cement. Sacks are generally one-fourth
barrel, or 95 lbs. Since empty barrels and sacks are
received by the manufacturer at a certain price, care
should be taken to preserve them in an orderly manner.
Empty sacks are most conveniently returned in bundles
of ten each.

Barrels and sacks should be marked by the manu-
facturer with name, trade-mark and gross weight of
package. Loss by sifting out and variations from
standard weight to the amount of 2 per cent are allow-
able.

STOBAGE (SEASONING) OF CEMENT.

Storage of cement improves its quality. If well pro-
tected and kept dry the cement gains in strength and
becomes more slow-setting and more constant in vol-
ume. This so-called seasoning results from the action
of the moisture and carbonic acid of the air. At the
same time, owing to the disintegration of the coarser
grains, the cement increases in fineness. If, however,
cement is stored in a damp place it becomes caked,
lumpy, partially set, and finally worthless. Dealers
should keep this in mind and, give close atten-

CHOICE OF CEMENT. 19

tion to the choice of a suitable place for btorage.
Portland cement bears long storage well, and even if
packed in sacks may be safely kept in a dry place for
many months.

If fresh, insufficiently seasoned cement is packed, an
increase of volume takes place on long storage, and if
the barrels are too completely filled or the hoops too
strongly driven the hoops may be broken or the staves
bent out. This may occur with faultless cements, and
has nothing to do with so-called swelling or cracking.

CHOICE OF CEMENT AND CONCRETE MATERIALS.

Quick-setting cements are used for work exposed to
leaching water, also for plastering and casts. For
all other purposes slow-setting cement is preferable.
Neat Portland cement is rarely used for mortar, and
only in case the work is to remain constantly under
water or in damp earth. In other cases more or less
sand must be used to prevent shrinkage-cracks and
produce a weatherproof mortar.

The character of the sand, gravel and stone used has
great influence on the strength of the work. The sand
must be sharp and pure; if it contains clay this must
be removed by repeated washing. Very fine sand is
generally objectionable; the best results are obtained
with a graded sand, consisting of grains of various
sizes, from fine to coarse. Stone and gravel for con-
crete must also be naturally clean or well washed, and
must not be soft or chalky. Only clean water, free
from mud, should be used for mixing cement mortar.

PREPARATION AND USE OP MORTAR.

If good results are to be obtained with Portland
cement great care must be taken in the preparation of
the mortar. If vessels which have been used for lime

20 PREPARATION AND USE OP MORTAR.

or contain set cement are employed these must be
well cleaned before use. As cement and sand are
mixed in proportions by measure, it is a good plan
to provide measuring vessels corresponding to the vol-
ume of the cement packages. The necessary figures
are given in a previous paragraph under "Packing and
Weight." Guess-work mixtures should never be made,
for such methods not only give mortar of varying com-
position, but also cause unnecessary waste of cement.

The proportion of sand to be used varies with the
character of the work*; 1 to 2 parts sand to 1 cement
are used only for work requiring extraordinary strength,
great resistance to wear, or impermeability to water; 3
to 4 parts sand to 1 part cement are employed for
ordinary weatherproof plastering, building mortar,
foundations, artificial stone, etc.

More or less water should be taken according to the
rate of setting of the cement, conditions of temperature,
and kind of work in view. As a general rule as little
water as possible should be used, and the mortar made
plastic by prolonged, vigorous mixing. For the prep-
aration of mortar the measured quantity of sand is
spread out and the correct amount of cement scat-
tered evenly over it; the two materials are then thor-
oughly mixed together. The necessary quantity of
water is then strongly and thoroughly worked into the
mass.

One of the chief rules in preparing mortar is that
cement which has become set should never be worked
up anew with water. For this reason no more mortar
should be mixed at one time than can be used before
the setting begins. Mortar which has become set and
is again made plastic with water will never gain its
normal hardness. Another important point is that the

CEMENT- LIME MORTAR. 21

brick or stone used for building must be thoroughly
wetted before being laid up with cement mortar. The
work should also be kept damp for a considerable time
after it is finished, in order that the mortar may reach
its full, stone-like hardness. The common practice of
wetting bricks just before use by sprinkling with water
from the mason's brush is quite insufficient. The bricks
should be kept under water, in a vessel, until thoroughly
saturated, and a stiff mortar used, in order that the
brick should not be displaced after laying.

OEMENT-LIME MOETAR.

There are many kinds of work which require a quick-
hardening mortar, but for which the great strength of
a mixture of 1 cement with 1 to 4 of sand is unneces-
sary. The cost of such mortar is also, for many pur-
poses, too high. A mixture of cement with 5 or more
parts sand would give abundant strength, but such
mortar works too " short '' and adheres too imperfectly
to the brick or stone ; it cannot, therefore, safely be used.

In such cases the addition of slaked lime or hydraulic
lime will correct the faults of poor mixtures of cement
and sand, and will produce a cheap mortar, suitable
for a great variety of uses. The addition of slaked
lime allows the full advantage to be obtained from the
use of good Portland cement, and makes it possible for
this material to compete in price with cheaper hydraulic
materials. Used in this manner, Portland cement may
be employed with economy for the most ordinary pur-
poses. The advantages of Portland cement lime mortar
are its cheapness in comparison with other hydraulic
materials, it rapid hardening, marked hydraulic prop-
erties, great strength on exposure to air, and remark-
able resistance to weather.

22 POKTLAND CEMENT MOETAR IN WATER AND AIR.

The following mixtures for cement-lime mortar have
been found by experience to be most suitable:

Cement 1, sand 5, lime paste %.

1, " 6 to 7, *' " 1

1, " 8, " " IK

" 1, " 10. " " 2

The above proportions are to be taken by measure.
Hydraulic lime may be used in place of ordinary slaked
lime.

Cement-lime mortar is prepared by making a dry
mixture of the required quantities of cement and sand;
milk of lime is then made with the necessary quanti-
ties of lime paste and water, and this milk of lime
thoroughly mixed and worked in with the mixture of
cement and sand.

The great advantages of cement-lime mortar for a
multitude of purposes deserve to be more widely
recognized than they are at present.

PORTLAND CEMENT MORTAR IN WATER AND IN AIR.

On account of its remarkable hydraulic properties,
great strength, and durability, Portland cement mortar
gives excellent results both in water and in air. The
first essential to success is, however, that the mortar
should be prepared and used suitably and intelligently
for the special purpose in view. For work to be
exposed to water, care must be taken to produce as
dense and impenetrable a surface as possible; this may
be accomplished by mixing the materials in suitable
proportions. Ornaments, casts, etc., which are to be
exposed to weather must never be made from pure
cement; the same may be said of architectural artificial
stone work. A certain proportion of sand must always
be added.

WATER-TIGHT MORTAR. 2o

In the preparation of water-tight mortar it should be
remembered that the richer the mixture is in cement
and the longer the mortar hardens the greater will be
it impermeability to water. The reason of this is that
in the process of hardening the mortar becomes con-
stantly more dense, and the pores gradually close.
The porosity of mortar is the greater, the thinner the
layer employed and the higher the proportion of sand
used. Coarse sand, also, gives a more porous mortar
than fine sand. For a coating f to | of an inch in
thickness which requires to be immediately water-
proof, the following mixtures are recommended:

Cement, 1, sand (not too coarse), 1

" 1, " 1, lime paste >^

1, " 3, " " 1

" 5, " " IM

" 6, « « 2

Which of these mixtures is to be employed depends
on the nature of the work. By the addition of gravel
or broken stone to the above mixtures water-tight con-
crete is obtained. From motives of economy, however,
it is customary to make only the surface of the concrete
of water-tight composition.

CEMENT PLASTERING AND PAINTING.

Experience has shown that cement plastering on walls
and cornices, even when made with faultless material, is
not always permanent. Sometimes the surface scales
off in thin layers; in other cases blisters form and crack,
or the whole layer of plastering may separate from the
wall and fall off. In all such cases the work, and not
the cement, is at fault. If walls are to be plastered with
cement mortar it is indispensable that the surface be
previously thoroughly cleaned from dust, dirt or lime-
mortar, washed and repeatedly wetted. If the wetting

24 CEMENT PLASTBBING AND PAINTING.

is insufficient the dry stone or brick take away from
the cement the water necessary for hardening; if this
happens the mortar adheres badly and never reaches
its proper hardness. Wall-plastering which is exposed
to weather should never be made very rich in cement
for fear of the formation of shrinkage cracks. The
more sand is used, provided the necessary strength is
obtained, the better the plastering will resist the
weather. Fine sand should be used, and for the pur-
pose of avoiding hair-cracks and shrinkage cracks it is
best to finish the surface with a felt polisher instead of
a trowel or steel tool.

Cement plastering must be kept moist and pro-
tected from wind and sun. This work can be done
most advantageously in spring; frost should be espec-
ially avoided. Some sands contain little particles of
coal which are scarcely visible to the eye; these may
have a very bad effect on the appearance of the work.

Cement work which is to be painted, either on account
of hair-cracks or efflorescences derived from the alkal-
ies and lime of the cement, or from any other cause,
must be fully hardened and thoroughly dry. It is
prudent to let the work stand a year before oil paint is
applied. To insure the durability of the painting
several methods may be used.

1. The surfaces are repeatedly brushed over with
dilute sulphuric acid (1 part strong acid to 100 parts
water), and allowed to dry before the paint is applied.

2. The surfaces are repeatedly and carefully washed
with water, then after 8 days, saturated twice with lin-
oleic acid (to be had from any druggist). After a few
days, when the surface has grown hard, the oil paint is
applied.

3. An excellent preparatory coating for oil paint is

CONCRETE. 25

a solution of common water-glass in 3 or 4 parts water.
After two applications the surface is washed with water;
after a short time the water-glass is again applied.
When dry the paint can be used.

Even oil paint is, however, often of slight durability
when exposed to weather. For work of great perman-
ence the patent process of Dr. Golinelli, Koch and
Adamy of Darmstadt, for preparation of cement work
for stereochromatic painting, may here be mentioned.

OONGRETE.

One of the most important uses of Portland cement
is in the making of concrete. This is a mixture of
cement with sand and gravel or broken stone, with the
addition of the necessary water. To obtain good ad-
hesion of the materials, the water, sand and stone must
all be clean; in some cases washing of these materials
may be necessary.

The gravel or stone used must be at least equal in
hardness to the cement mortar. Good gravel, basalt or
hard lime stone are most suitable; soft sandstone or
broken brick are to be avoided. The stone should not
be above egg size. The proportions to be used depend
on the nature of the work. When once determined
they should be rigidly adhered to. For the preparation
of concrete, the cement and sand are well mixed
together on a dry platform; enough water is then mixed
in to make the mortar about as moist as damp garden-
earth; the gravel or stone, previously well wetted, is
then added, and the whole thoroughly mixed by
repeatedly turning over with shovels. The proportion
of water must be so regulated that after prolonged and
vigorous stamping the mass will become elastic and
show a little water on the surface. The use of more

26 PREPARATION OF CONCRETE FLOORS, ETC.

water is to be ayoided, since it makes the mass less
dense and lowers its strength. Too great stress cannot
be laid upon thorough and careful stamping of the con-
crete into place, since in no other way can great strength
and density be obtained.

With good Portland cement the proportion of 1 part
cement and 3 parts sand, with varying amounts of
gravel or stone up to 9 parts, will be found suitable;
for some purposes poorer mixtures may be used.

Portland cement concrete finds many useful applica-
tions in constructions both above and below ground;
for example, in foundations of all kinds, sidewalks,
ceilings, walls, arches, cement wares, etc.

PREPARATION OF OONORBTE FLOORS, SIDEWALKS, STEPS
AND CEILINGS.

For the construction of durable cement floors or side,
walks the foundation must be suitably prepared. For
outdoor work on yielding ground a porous layer, at
least 10 inches thick, of coarse gravel or slag should be
laid, well rammed down and leveled. For indoor work
on dry ground it is sufficient to level the surface and
stamp it down firmly. Floors and sidewalks are gen-
erally built in two layers; a lower bed of concrete 2^
to 4 inches thick, and a surface coat of richer mortar
of a thickness of f to f of an inch.

The concrete layer may be made richer or poorer
according to the service which the work must undergo.
For heavy duty a mixture of cement 1, sand 3 and gravel
6 is recommended. In less important work cement 1,
sand 5 and gravel 10 will answer. A suitable mixture
for ordinary requirements is, cement 1, sand 4 and
gravel 8 or broken stone 6.

The surface layer consists of cement 1, sand 1, and

PREPARATION OF CONCRETE FLOORS, ETC. 27

must be spread over the concrete before the latter has
set. Before spreading the top layer the concrete should
be freed from loose material and its surface roughed
up. The mortar is spread with a straight-edge and
when sufficiently hardened is finished with a wooden
tool. A grooved roller is used to produce a ribbed sur-
face, especially in side-walk work.

When the work is finished and the cement is well set,
the surface is carefully covered with a layer of sand 4
inches in thickness. This is moistened and kept in
place for several weeks if possible. Only in this way
can the formation of hair-cracks be prevented and a
well hardened surface obtained.

Cement expands and contracts with changes of tem-
perature, in the same way as iron, wood, sandstone and
other materials. From this cause, if the necessary care
has not been taken in the work, cracks will result,
especially in wide surfaces. These may be avoided by
dividing the flooring into smaller blocks, which should
not exceed 4 to 5 square yards in area, and should be
separated by strips of tar paper or by sand joints f inch
in width. The joints in the concrete must correspond
with those cut in the surface layer. The division of
the work into blocks is also to be recommended in con-
crete walls and curbs.

One of the most strikingly successful applications of
Portland cement in building is its use for ceilings and
staircases. Safety against fire, freedom from dry-rot,
quickness of construction, and cheapness are some of
the many advantages presented by this type of con-
struction. A description of this and other similar
applications of cement would, however, extend this
pamphlet beyond desirable limits. Reference must,
therefore, be made to special works on this subject.*

28 NOTES ON CEMENT WORK AND ITS TREATMENT.

As already stated, cement work must be protected
from too rapid drying out, since from this cause shrink-
age cracks and lack of hardness and strength may
result. A certain amount of water is absolutely neces-
sary for the proper hardening of cement.

In case of sidewalks, ceilings, etc., the surface is to
be kept covered with damp sand as long as possible.
Cement wares should be kept under water, or stored in
damp rooms, free from currents of air, and frequently
sprinkled. Wall-plastering should be kept covered as
long as possible with wet sacks or cloths. Cement
casts which are to be exposed to weather, such as
statues and architectural ornaments, must never be
made of pure cement; a suitable proportion of sand is
necessary, even for the surface. By the addition of
fine, sharp sand the formation of unsightly hair-cracks
is avoided without injury to the appearance of the
work. The use of quick-setting cement with too little
sand and much water, taking the objects too soon out
of the moulds, and their delivery before they have
acquired the necessary hardness, are serious errors.
Such treatment was formerly much more common than
it is at present, and has done much to cause cement
wares to be regarded with undeserved suspicion. Since
the introduction of more rational methods of manu-
facture, casts in cement have given full satisfaction,
and owing to their cheapness are rapidly coming into
extensive use. Architectural details for which sand-
stone was exclusively used twenty years ago, are now
extensively cast in cement and find application in edi-
fices of the most highly artistic character.

♦Portland cement und seine Anwendungen im Bauwesen; Berlin, 1892.
'~'ement in seiner Verwendung im Hochbau; Liebold, Halle, 1875.

CONCLUSION. 29

In conclusion it may be noted that the remarkable
properties of Portland cement make it suitable for an
endless variety of uses. It is hoped that this brief
sketch may serve to bring this valuable material into
more extensive notice, and to contribute to a wider
appreciation of its qualities and capabilities.

MAR 19 1§04

Cement and Engineering Aleivs

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